1. Field of the Invention
The invention relates to a display device having a thin film transistor.
2. Description of the Related Art
A conventional liquid crystal display device (referred to as LCD, hereafter) has a plurality of pixels arrayed in a matrix of n rows and m columns, and each of the pixels includes a pixel selection thin film transistor 10 (referred to as a TFT 110, hereafter), a liquid crystal LC, and a storage capacitor Csc, as shown in FIG. 14. It is noted that FIG. 14 shows only the pixels in two rows and two columns for simplification of the figure.
A gate line 120 extending in the row direction is connected to a gate of the TFT 110, and a drain line 121 extending in the column direction is connected to a drain thereof. A gate scan signal is supplied from a vertical drive circuit (V drive circuit) 130 to the gate line 120 in each of the rows sequentially, and the TFT 110 is selected in response to this signal. A video signal is supplied to the drain line 121 in response to a horizontal scan signal from a horizontal drive circuit (H drive circuit) 140, and applied to the liquid crystal LC through the TFT 110. This changes the alignment state of liquid crystal molecules to make a display. The storage capacitor Csc is used for storing the video signal supplied through the TFT 110.
The TFT 110, the gate line 120, the drain line 121, the vertical drive circuit (V drive circuit) 130, and the horizontal drive circuit (H drive circuit) 140 are formed on a TFT substrate, and the liquid crystal LC is sealed between this TFT substrate and a common substrate.
Light of a backlight enters from the TFT substrate side to the LCD.
The relevant technology is disclosed in the Japanese Patent Application Publication No. 2004-165241.
In recent years, the luminance of light from the backlight is increasing together with the realization of higher resolution and higher color rendering of the LCD. Since light from the backlight generally enters from the TFT substrate side in a direct-view type LCD and thus a leak current in the TFT 110 irradiated with the light of the backlight increases, electric charge stored in the storage capacitor Csc leaks to cause degradation in contrast, a flicker, or a crosstalk, thereby providing a problem of degradation in a display quality. In a case where the intensity of incident light is extremely high like in a liquid crystal projector or a head-up display on a vehicle or in a case where there is a need to take into account light entering from both the sides of a liquid crystal panel, not only the incident light but also light reflected by the surface of the TFT substrate (a glass substrate) enters the TFT 110. Therefore, the leak current of the TFT 110 increases, thereby providing a problem of degradation in a display quality in the same manner as above.